1. Field of the Invention
The present invention relates to a hydraulic control valve which controls hydraulic fluid supplied to a rotator such as a hydraulic motor that is installed in an excavator or the like.
More particularly, the present invention relates to a hydraulic control valve which can prevent the occurrence of overload by relieving hydraulic fluid of a return line in which the overload occurs due to an inertial force of a rotator when a hydraulic motor that is operated by the hydraulic fluid supplied from a hydraulic pump stops halfway.
2. Description of the Prior Art
As illustrated in FIG. 1, a conventional hydraulic control valve includes a valve block 1 in which a first pump path 3 to which hydraulic fluid from a hydraulic pump P is supplied and second pump paths 4 and 5 which are connected in parallel to the first pump path 3 are formed; a spool 2 shiftably coupled to the valve block 1 by pilot signal pressures Pi1 and Pi2 from the outside and shifted to control the hydraulic fluid supplied from the hydraulic pump P to a hydraulic motor (not illustrated); first and second actuator paths 8 and 9 connecting the second pump paths 4 and 5 to first and second actuator ports 6 and 7, respectively, in accordance with the shifting of the spool 2; and a relief valve 10, if overload occurs in either of the first and second actuator ports 6 and 7, relieving the hydraulic fluid in one of the first and second actuator ports 6 and 7 in which the overload occurs and providing a supplement supply of the relieved hydraulic fluid to the other of the first and second actuator ports 6 and 7 in which the overload does not occur.
The operation of the conventional hydraulic control valve as constructed above will now be described with reference to the accompanying drawings.
A) In the case where a spool of a direction change valve is shifted in the right direction as shown in the drawing:
As illustrated in FIGS. 1 and 3, if the pilot signal pressure Pi1 from the outside is supplied to a left port as shown in the drawing, the spool 2 is shifted in the right direction. Hydraulic fluid discharged from the hydraulic pump P flows through the first pump path 3 and the second pump path 4 in order, and then is supplied to the first actuator port 6 via the first actuator path 8. Accordingly, the hydraulic fluid is supplied to the hydraulic motor to rotate the rotator clockwise or counterclockwise.
At this time, hydraulic fluid returning from a hydraulic motor flows into the second actuator port 7, and then returns to a hydraulic tank (not illustrated) via the second actuator path 9 and a tank path 11 in order.
On the other hand, if the spool 2 is shifted to its neutral position while the hydraulic motor is rotated by the hydraulic fluid supplied from the hydraulic pump P, the rotator of the hydraulic motor is unable to stop straight due to an inertial force of the rotator to cause the occurrence of overload in the second actuator port 7.
At this time, the hydraulic fluid on the side of the second actuator port 7 passes through a third check valve 12, and is relieved by the relief valve 10. The relieved hydraulic fluid is supplied to the first actuator path 8 via a second check valve 13, and thus the shortage of hydraulic fluid on the side of the first actuator port 6 can be supplemented.
B) In the case where the spool of the direction change valve is shifted in the left direction as shown in the drawing:
As illustrated in FIGS. 1 and 3, if the pilot signal pressure Pi2 from the outside is supplied to a right port as shown in the drawing, the spool 2 is shifted in the left direction. Hydraulic fluid discharged from the hydraulic pump P flows through the first pump path 3 and the second pump path 5 in order, and then is supplied to the second actuator port 7 via the second actuator path 9. Accordingly, the hydraulic fluid is supplied to the hydraulic motor to rotate the rotator clockwise or counterclockwise.
At this time, hydraulic fluid returning from the hydraulic motor flows into the first actuator port 6, and then returns to the hydraulic tank via the first actuator path 8 and a tank path 14 in order.
On the other hand, if the spool 2 is shifted to its neutral position while the hydraulic motor is rotated by the hydraulic fluid supplied from the hydraulic pump P, the rotator of the hydraulic motor is unable to stop straight due to the inertial force of the rotator to cause the occurrence of overload in the first actuator port 6.
At this time, the hydraulic fluid on the side of the first actuator port 6 passes through a first check valve 15, and is relieved by the relief valve 10. The relieved hydraulic fluid, which is supplied to the second actuator path 9 via a fourth check valve 14, supplements the shortage of hydraulic fluid on the side of the second actuator port 7.
On the other hand, if the overload occurs in the first actuator port 6 or the second actuator port 7 by an external force applied from the outside even in the state where the spool 2 is maintained in its neutral position, the occurrence of the overload can be prevented in the same manner as described above.
As shown in FIG. 2, since the above-described first and third check valves 15 and 12 are mounted on the lower end parts of the control valve, the workability on manufacturing and assembling of the control valve is degraded with the manufacturing cost increased, and thus the competitiveness of the product is weakened in the same industrial field.
In addition, in the case of inspecting the first and third check valves 15 and 12 after installing the control valve in the equipment, it is required to take away the whole control valve from the equipment.